Such rotary encoders are known per se, and typically include a code wheel, mounted to a first one of the relatively rotatable bodies, having a plurality of radially extending, circumferentially spaced lines, situated at equi-angular intervals about the periphery of the code wheel, thereby to form a scale. An optical readhead, mounted to the other of the relatively rotatable bodies, and in register with the scale, projects light onto the scale which, depending upon the configuration of code wheel, is then either reflected or transmitted. From the reflected or transmitted light, the readhead generates a series of signals which may be used to generate an incremental count indicative of the relative angular displacement of the first and second relatively rotatable bodies.